1. Field of Invention
The present invention relates generally to methods and compositions creating an earthen hardpan and more specifically to an earthen hardpan useful for sealing ponds, and/or drilling pits.
2. Description of Prior Art
There currently are two main systems for the sealing of ponds. The first system makes use of natural materials, such as clay minerals or more specifically Na-bentonite, or soils rich in clay, salts or polymers (Prickett, 1968, FAO; Wilson, K. J., 1966, Am. Soc. of Civil Eng. Denver; Banin, A., 1976, Fac. Agri. Heb. Univ. Jerusalem; Garbotz, G., 1966. Con. Jour.).
The second system is based on the use of artificial coverings of ponds, for example asphalt, plastic films made of polyethylene, P.V.C., synthetic rubber and the like.
The first system has historically suffered from seepage of water, reaching several percentages of water loss per volume. In cases in which sewage water is restored there exists the danger that such water will reach the aquifer and contaminate it. The artificial materials used for sealing are more reliable but are much more expensive than the natural ones.
In many studies, the combination of soil material and clay with the addition of Na salts, was found to minimize the hydraulic conductivity of porous media. However, the exact percentages of clay and sand were not specified. Absolute saturation of the clay by Na was never attained, nor obviously the absolute sealing of the soil, and its application for water reservoirs.
More recently, a method of sealing ponds was described in U.S. Pat. No. 4,647,259, where the water impervious layers are produced from mixtures of sand (about 90 to 98.5 weight percent) and montmorillonite ((Na, Ca) (Al, Mg)6 (Si4O10)3 (OH)6—nH2O, hydrated sodium calcium aluminum magnesium silicate hydroxide) (about 1.5 to 10 weight percent), which are compacted and contacted with salt water having a salt content at least equal to that of sea water, and the layers are then washed until no further Na comes off the layers.
To form a hardpan or water barrier in a soil requires clay and multivalent cations such as calcium and magnesium. These cations, when in solution with the clay particles, form chelates and aggregate. The aggregate form a water impermeable layer when sufficiently dense. Perched water tables form over these hardpans. How quickly a hardpan forms depends an the clay content and the cation content.
Bentonite clay has been successfully used as a pond sealant for many years. Dry ponds have been lined with bentonite clay as standard procedure when leaks cannot be tolerated. When fresh water is added to bentonite clay it will expand to 18 times its normal volume in the dry state. However, in arid climates, the water eventually evaporates from the bentonite causing it to dry and crack and create new fissures for leakage to occur when liquid is reintroduced to the pond or well site.
Until the present invention, there has not been available a method for sealing ponds using bentonite or other clays in combination with monovalent and divalent cations that will not dry and crack in a low moisture environment.